Dryer control system



Feb. 21, 1967 M. A. NELSON DRYER CONTROL SYSTEM 2 Sheets-Sheet 1 Filed Oct. 22, 1965 FIGZ INVENTOR MAX A. NELSON BY W QM AGENT Feb. 21, 1967 M. A. NELSON DRYER CONTROL SYSTEM 2 Sheets-Sheet 2 Filed Oct. 22, 1965 FIG.4

INVENTOR MAX A. NELSON AGENT United States Patent Ofiice fid ldiizl Patented Feb. 21, 1967 3,394,621 DRYER CUNTRGL SYSTEM Max A. Nelson, Logansport, Ind, assignor to Essex Wire Corporation, Fort Wayne, End, a corporation of Michigan Filed Oct. 22, 1965, Ser. No. 509,253 Claims. (Cl. 3445) This application is a continuation-in-part of my copending application Serial No. 420,560, filed December 23, 1964, now abandoned, for Dryer Control System.

This invention relates to domestic clothes drying machines and more particularly to an electrical control system used in such machines.

In the past, it has been proposed to terminate the drying of clothes in clothes drying machines in response to the actual moisture condition of the clothes. One previous dryer control system used a moisture-responsive control which measured the resistance of the cloth-es being dried. The moisture-responsive control initiated operation of a timer when the resistance of the clothes remained above a predetermined value for a certain time interval. The timer then terminated operation of the dryer at the end of a short time interval of continued dryer operation. During this last time interval, the moisture-responsive control was inoperative. As certain types and weights of clothes gave a false indication of dryness, the above described control system was not always effective when completely dried clothes were desired.

Accordingly, it is an object of this invention to provide a dryer control system of the type having a moistureresponsive control which senses the electrical resistance of the clothes being dried, which initiates termination of the drying operation when the electrical resistance of the clothes is above a predetermined value during a first predetermined time interval, and which terminates the drying operation when the electrical resistance of the clothes remains above said predetermined value during a second time interval following the first time interval.

Another object of this invention is to achieve the abovementioned object by a control system in which the desired sequence of operation is repeated if interrupted at any time by opening of a dryer door interlock switch.

Other objects and advantages of the invention will be come apparent with reference to the following description of the preferred embodiment of the invention illustrated in the accompanying drawing in which:

FIGURE 1 is a schematic diagram of a circuit illustrating a dryer control system embodying the invention;

FIGURE 2 is a side elevational view of a relay used in the dryer control system;

FIGURE 3 is an end elevational view of the relay shown in FIGURE 2; and

FIGURE 4 is a schematic diagram of a modification of the system of FIGURE 1.

Referring first to FIGURE 1 of the drawing, there is shown a dryer control system for controlling the energization of a heating unit 10 and an electrical motor 11 from the usual power supply lines 12 and 13. The heating unit it) may be an electric heating coil or the coil of an electromagnetic valve which controls the flow of gas to a gas burner. The motor ll may rotatably drive the usual drum or basket containing clothes to be dried and also may drive the usual fan or blower for forcing heated air into the drum. The motor 11 includes a main winding 14 and a starting winding 15 both connected at a common end to a junction 16. The other ends of the windings 14 and 15 are connected in parallel by the contact arm 17 and the contact 18 of a speed-responsive switch 19. The switch 19 is controlled by a centrifugal mechanism 20 responsive to the speed of the motor 11 which moves contact arm 17 from engagement with contact 18 into engagement with a contact 21 when the motor 11 attains a certain speed upon starting. The contact 21 is connected by a thermostatic switch 22 to the line 13. The thermostatic switch 22 which is responsive to the temperature of the air heated by the heating unit 10 closes when the air temperature rises above a predetermined value and opens at a temperature below that value. The thermostatic switch 22 provides for continued operation of the motor 11 for a limited period of time after the heating unit is deenergized. The junction 16 is connected to the line 12 by a conventional door switch 23 which is closed when the dryer door is closed and opened when the dryer door is open to prevent operation of the motor 11 with the door open. The control system includes two relays 24 and 25 of conventional construction. The relay 24 has two normally open switches 26 and 27 which are closed when the relay coil 28 is energized. The relay 25 has a single normally closed switch 29 which is opened when the relay coil 30 is energized.

An important component of the control system is a third relay 31 having in addition to the usual normally open and normally closed contacts a third set of contacts which are mechanically held in either closed or open position when the relay is deenergized and which are transferred between open and closed positions by successive energizations of the relay. While the construction of the relay 31 is subject to variation, a preferred construction is shown in detail in FIGURES 2 and 3. The relay 31 includes the usual alternating current electromagnet structure consisting of a magnetic frame 32 mounted upon a base 33, a magnetic core 34 secured to the frame 32 and carrying a copper shading ring 35 at its end, a coil 36 surrounding and fixed to the core 34, and an armature 37 pivotally supported upon the frame 32 and biased away from the core 34 by a spring 38. The two coil leads are soldered or welded to the terminals 39 and 40. A stack of contact springs 41, 42, 43, 44, 45, and 46 held between a plurality of insulator blocks 47 is supported upon a shelf extension 48 of the frame 32. The contact ends of the contact springs 42, 43, and 46 are movable and cooperate with relatively stationary contact ends of the contact springs 41, 44, and 45, respectively. It is to be noted that the supported ends of the contact springs 44 and are held in permanent electrical engagement with each other.

An actuator plate 49 of insulating material is rigidly fixed to the movable end of the armature 37. The plate 49 is provided with two narrow horizontal slots 50 and 51 into which the free ends of the contact springs 42 and 43 project to he flexed by movement of the armature 37. A cam and ratchet wheel 52 of nylon or other insulation material is rotatably supported on a stud 53 which is rigidly secured to the plate 49. A pawl 54 secured to the base 33 has a resilient arm arranged for ratcheting engagement with the twelve ratchet teeth 55 of the wheel 52 so as to advance the wheel one-twelfth of a revolution each time the armature 37 is attracted to the core 34. Another pawl 56 secured to the plate 49 has a resilient arm in holding engagement with the ratchet teeth 55 to prevent reverse rotation of the wheel 52. The wheel 52 also has siX cam teeth 57 each having a flat breast 58 meeting a flat top 59 at an obtuse angle. The cam teeth 57 and the ratchet teeth 55 are so arranged that the breasts 5% and the tops 59 of the cam teeth 57 are alternately center-ed opposite the center of the rectangular slot 60 in the plate 49. The free end of the contact spring 46 extends through the slot as and resiliently engages the lower edge of the slot 60 with the wheel 52 in the position shown in FIGURE 3.

With the parts of the relay 31 in their respective positions shown in the drawing, the contact springs 41 and 42 are engaged, the contact springs 43 and 44 are separated, and the contact springs 45 and 46 are separated. When the coil 36 is energized, the armature 37 is attracted to the core 34, causing separation of the contact springs 41 and 42 and engagement of the contact springs 43 and 44. At the same time, the engagement of a ratchet tooth 55 by the pawl 54 advances the wheel 52 one-twelfth of a revolution thereby rotating the top 59 of a cam tooth 57 into engagement with the contact spring 46. When the coil 36 is then deenergized and the armature 37 is returned to its unattracted position by the spring 38, the contact spring 46 is shifted by the top 59 into engagement with the contact spring 45. At this time, the contact springs 41 and 42 reclose and the contact springs 43 and 44 reopen. When the coil 36 is next energized, the armature 37 causes the contact springs 45 and 46 to separate and the wheel 52 to rotate another one-twelfth of a revolution. This again centers abreast 58 of a cam tooth 57 under the slot 60; and when the armature 37 returns to its unattracted position, the contact springs 45 and 46 will remain separated. Thus, it will be seen that the contact springs 45 and 46 will be engaged only during every alternate deenergization of the relay coil 36. The contact springs 41 and 42 and the contact springs 43 and 44 open and close as in a conventional relay.

Referring again to FIGURE 1, a manually operated momentary start switch 61 is shown as having two sets of normally open contacts 62 and 63 connected in series between the supply line 13 and a junction 64. The contact springs 45 and 46 are also connected between the supply line 13 and the junction 64. Connected in parallel with the contacts 62 of the start switch 61 is the switch 27 of the relay 24 which has one end connected to the supply line 13 and the other end connected by a conductor 65 to the junction 66 of the contacts 62 and 63. The other contacts 63 of the start switch 61 are shunted by the contact springs 43 and 44 which are connected between the junctions 64 and 66.

Connected between the supply line 12 and the junction 64 is a moisture-sensing circuit including a rectifier 67 connected on one side to the junction 64 and on the other side through an adjustable resistor 68 to a conductor 69. A capacitor 70 is connected between the conductor 68 and the supply line 12 and thus may be gradually charged through t-he resistor 68 and the rectifier 67. The capacitor 70 is shunted by a gaseous discharge device 71 such as a neon glow tube through the coil 30 of the relay 25. The discharge device '71 has a definite breakdown potential at which it becomes conductive. When the voltage across the capacitor 70 builds up to the breakdown potential of the discharge device '71, the capacitor 76 discharges through the discharge device 71 and the relay winding 36, causing the relay switch 29 to open. The contact springs 41 and 42 of the relay 31 are connected in series with a current limiting resistor 72 across the capacitor 79 so that the latter is discharged and cannot be recharged as long as the contact springs 41 and 42 remain closed. Also shunting the capacitor 76 is a pair of electrodes 73 and 74 which are mounted within a dryer drum rotated by the motor 11. The electrodes 73 and 74 may comprise suitably insulated wires exposed to the clothes contained in the dryer drum such as is described in Great Britain Patent No. 877,553 issued September 13, 1961, to the Maytag Company. Damp clothes coming into engagement with the electrodes 73 and '74 electrically bridge or short the electrodes and thus discharge the capacitor 70.

The operation of the dryer control system shown in FIGURE 1 will now be described. Initially, the system is in the normal or deenergized condition in which the coils of the relays 24, 25, and 31 are deenergized and their contacts are in the positions in which they are illustrated. The capacitor 70 is fully discharged as it is shunted by the resistor 72 through the closed contact springs 41 and 42. When wet or damp clothes are placed in the dryer drum and the start switch 61 is momentarily closed to initiate dryer operation, the coil 28 of the relay 24 is initially energized in a circuit extending from the supply line 13 through the contacts 62 of the start switch 61, junction 66, contacts 63, junction 64, coil 28 and door switch 23 to the supply line 12. The energization of the relay coil 28 causes the relay switches 26 and 27 to close. The relay switch 26 completes a circuit connecting the heating unit 10 across the supply lines 12 and 13. At the same time, the relay switch 27 completes a circuit to the main winding 14 of the motor 11 extending from the supply line 13 through the relay switch 27, main winding 14, junction 16, and the door switch 23 to the supply line 12. As the starting winding 15 is connected in parallel with the main winding 14 by the contact arm 17 and the contact 18, the motor 11 starts. As the motor 11 comes up to speed, the contact arm 17 separates from the contact 18 and engages the contact 21 thereby disconnecting the starting winding 15 and connecting the thermostatic switch 22 in .parallel with the relay switch 27.

The momentary closing of the start switch 61 also energizes the coil 36 of the relay 31 in a circuit extending from the supply line 13 through the contacts 62, junction 66, contacts 63, junction 64, coil 36, and switch 29 of the relay 25 to the supply line 12. The energization of the relay coil 36 causes the contact springs 43 and 44 to close thereby establishing a holding circuit across the contacts of the starting switch 61. This holding circuit extends from the supply line 13 through the switch 27 of relay 24, conductor 65, junction 66, the contact springs 43 and 44 to the junction 64. The energization of the relay coil 36 also causes the contact springs 41 and 42 to open, thereby allowing the capacitor 70 to charge. The charging circuit for the capacitor 70 extends from the supply line 13 through the relay switch 27, conductor 65, junction 66, contact springs 43 and 44, junction 64, rectifier 67, resistor 68, conductor 69 and capacitor 70 to the supply line 12. During initial operation of the dryer, the capacitor 70 is repeatedly if not continuously discharged by the engagement of damp clothes with the electrodes 73 and '74. The capacitor 70 therefore does not charge to a voltage suflicient to cause breakdown of the discharge device 71. As the dryer operation continues, the electrical resistance of the clothes increases considerably and there will be little or no discharging of the capacitor 70 across the electrodes 73 and 74, permitting the capacitor 7 6 to gradually charge at a rate determined primarily by the values of the resistor 68 and the capacitor 70. When the capacitor 70 is charged to a voltage equal to the breakdown potential of the discharge device 71, the latter suddenly becomes conductive. The capacitor 79 then discharges through the discharge device 71 to energize the coil 30 of the relay 25, thereby causing the momentary opening of relay switch 29.

The opening of relay switch 29 deenergizes the coil 36 of the relay 31 causing the contact springs 41 and 42 to reclose, the contact springs 43 and 44 to reopen, and the contact springs and 46 to close. The opening of the contact springs 43 and 44 interrupts the holding circuit of the relay coil 36 extending between the supply line 13 and the junction 64 but this opened holding circuit is now shunted by the closed contact springs 45 and 46. Consequently, the coil 28 of the relay 24 remains energized. The closing of the contact springs 41 and 42 completes a discharge circuit for the capacitor through the resistor 72 which discharges the capacitor 70 almost instantly. This deenergizes the relay coil 30 and the relay switch 29 recloses to establish an energizing circuit for the coil 36 of the relay 31 extending from the supply line 13 through the contact springs 46 and 45, junction 64, coil 36 and relay switch 29 to the supply line 12.

When the coil 36 is thus energized again, the contact springs 41 and 42 open, the contact springs 43 and 44 close, and the contact springs 45 and 46 open. The holding circuit for the relay coil 36 is again established through the relay switch 27 and the contact springs 43 and 44 while the capacitor discharge circuit through the resistor 72 is again interrupted. This renders the moisture-sensing circuit effective again with the capacitor 70 connected through the relay coil 38 across the discharge device 71. After a predetermined period of time during which no damp clothes bridge the electrodes 73 and 74, the voltage across the capacitor 70 again reaches the firing potential of the discharge device 71 and the capacitor 70 discharges through the discharge device 71 and the relay coil 38. As a result, relay switch 29 again opens to deenergize the coil 36 of the relay 31. The contact springs 43 and 44 again open in response to deenergization of the coil 36 and interrupt the energizing circuits of the relay coil 36 and the relay coil 28. As the contact springs 45 and 46 are not closed by this second deenergization of the coil 36, the relay coil 28 is deenergized causing the relay switches 26 and 27 to open. The opening of the relay switch 26 deenergizes the heating unit 18 but the motor 11 remains energized through the shunt circuit provided by the thermostatic switch 22, the contact 21 and the contact arm 17. The thermostatic switch 22 was previously actuated to its closed position by heated air with the dryer and allows continued operation of the motor to circulate unheated air through the dryer drum. After a short time, the thermostatic switch 22 cools and opens to terminate the dryer operation. In this manner, a complete automatic cycle is provided, the dryer being fully shut oiI at the end of the cycle.

It will be seen that the second time delay period provided by the moisture-sensing circuit insures that the clothes are completely dried. The heating unit 11) remains energized during a second drying period after the electrical resistance of the clothes exceeds a predetermined value for a first predetermined period of time. Heavy clothes such as cotton rugs and towels may contain a great deal of moisture even though the outer surfaces may be quite dry. The second drying period following the sensing of an apparently dry condition allows such clothes to be thoroughly dried. It should also be noted that the moisture-sensing circuit is effective during the second time delay period and will extend operation of the dryer if damp clothes previously trapped in dry clothes come into engagement with the electrodes 73 and 74. The length of the time delay periods may be varied for different types of clothes by adjusting the resistance value of the resistor 68.

At any time during dryer operation when the door switch 23 is opened by the opening of the dryer door, the energizing circuits of the motor 11 and the relay coil 28 are interrupted. The deenergization of the relay coil 28 causes the relay switches 26 and 27 to open, deenergizing both the heating unit 18 and the motor 11. At the same time, the opening of relay switch 27 interrupts the holding circuit to relay coil 36 through the relay switch 27, conductor 65 and the closed contact springs 43 and 14. If the first time delay period described above has not been completed, the contact springs 45 and 46 are closed when the armature 37 of the relay 31 returns to its unattracted position. The closing of contact springs 45 and 46 immediately re-energizes the relay coil 36 whereupon the contact springs 45 and 46 separate and again deenergize the relay coil 36. When the armature 37 again returns to its unattracted position, the contact springs 45 and 46 remain separated. The parts of the relay 31 are then in the positions shown in the drawing and ready to repeat the entire above-described cycle of operation when the door switch 23 is reclosed and the start switch 61 is momentarily closed. If, on the other hand, the first time delay period has been completed when the door switch 23 is opened, the parts of the relay 31 return to the positions shown in the drawing when the relay coil 36 is deenergized by the opening of the relay switch 27. In

6 either case, when the door switch is reclosed and the start switch is operated, the dryer control system will repeat its entire operating cycle described above.

Although the relay 25 has been described as controlled by a particular moisture-sensing circuit, it is apparent that other moisture-sensing circuits will operate equally as well. It is also apparent that such moisture-sensing circuits may be utilized to control other types of switching devices such as semiconductor controlled rectifiers in place of the relay 25.

FIGURE 4 illustrates another embodiment of the invention. In this arrangement a stepping relay has been substituted for the relays 24 and 31. Most of the components of the embodiment of FIGURE 4 are identical with those in the FIGURE 1 arrangement and have been identified with the same reference numerals.

The relay 88 is a stepping ratchet relay having a springbiased armature 81 that acts to rotate a toothed ratchet wheel 82 a fixed amount each time the relay magnet coil 83 is energized and the same fixed amount each time the relay coil 83 is deenergized. The wheel 82 carries a shaft 84 having secured thereon four switch operating cams 85, 86, 87, and 88. The cams 85, 86, 87, and 88 control switches 89, 98, 91, and 92, respectively, which are opened and closed during each operating cycle of the relay 88 in the manner described below.

A manually operated momentary start switch 61a is connected in series between the supply line 13 and a junction 64a. One end of the relay coil 83 is connected to the junction 64a and the other end is connected by the relay switch 29 to the common conductor 93 of the moisture-sensing circuit. Conductor 93, in turn, is connected to the junction 16a. The relay switch 89 is connected in series with the current limiting resistor 72 across the capacitor 70 while the relay switch 90 is connected in parallel with the start switch 61a. The relay switches 91 and 92 connect the motor winding 14 and the heating unit 1-8 to the supply line 13. A normally open switch 19a controlled by the motor centrifugal mechanism is connected in series with the heating unit 18 to allow energization of the heating unit 10 only when the motor 11 is operating.

The operation of the FIGURE 4 dryer control system is basically the same as that of the FIGURE 1 system, the relay 88 providing the same switching action as that of the relays 24 and 31 of FIGURE 1. With the system in its normal or deenergized condition shown in FIGURE 4, the momentary closing of the start switch 61a initiates dryer operation by energizing the relay coil 83. The armature 81 then rotates ratchet wheel 82 one step clockwise causing shaft 84 and cams 85, 86, 87, and 88 to rotate one step of 90. The cam switch 89 opens and the cam switches 98, 91, and 92 close. This switching action establishes a holding circuit for the relay coil 83 through the cam switch 98, relay switch 29 and the door switch 23. At the same time the motor windings 14 and 15 are energized through the cam switch 91. The closing of the motor switch 19a completes an energizing circuit to the heating unit 10 through the cam switch 92 when the motor 11 comes up to speed. The opening of the cam switch 89 also disconnects the discharge resistor 72 from the capacitor 78, thereby rendering the moisture sensing circuit effective.

After the clothes in the dryer drum have sulficiently dried after continued dryer operation, the voltage across the capacitor 70 reaches the firing potential of the discharge device 71 and the capacitor 70 discharges through the discharge device 71 and the relay coil 38. The result ing energization of the coil 30 causes the relay switch 29 to open thereby deenergizing the relay coil 83. The relay armature 81 then returns to its unattracted position, rotating ratchet Wheel 82 one more step. The corresponding rotation of the cams recloses the cam switch 89, reopens the cam switch 91 but causes no change in the condition of the closed cam switches 90 and 92. As an alternate energization circuit for the motor winding 14 was previously completed by the closing of the centrifugal switch contacts 17, 21, and the thermostatic switch 22, the motor 11 remains in operation.

The closing of the cam switch 89 completes a discharge circuit for the capacitor 70 through the resistor 72 thereby deenergizing the relay coil 30. The reclosing of the relay switch 29 re-establishes the energizing circuit for the relay coil 83 which again attracts the relay armature 81. This causes the shaft 84 and the cams to rotate a further step of 90. The cam switch 89 re-opens while the other cam' switches remain in their previous condition.

The opening of the cam switch 89 renders the moisture sensing circuit effective again. After continued operation of the dryer for a predetermined period of time during which no damp clothes bridge the electrodes 73 and 74, the relay switch 29 will again be opened by the discharge of the capacitor 70 through the discharge device 71 and the relay coil 30. This again deenergizes the relay coil 83 permitting the armature 81 to return to its unattracted position. The armature 81 rotates the shaft 84 and the cams 8588 a final step to their original positions shown in FIGURE 4. The cam switch 92 opens to deenergize the heating unit 10. After a short time, the thermostatic switch 22 cools and opens to terminate the dryer operation.

If the door switch 23 is opened by opening of the dryer door at any time during dryer operation, the motor energizing circuit is interrupted. At the same time, the opening. of the motor centrifugal switch 19a as the motor 11 slows deenergizes the heating unit 10. The relay coil 83 will also be deenergized by opening of the door switch 23. If the first drying period has been completed at the time the door switch 23 was opened, the relay cams 85 88 are returned to their initial positions shown in FIG- URE 4. Upon reclosing of the door switch 23 and momentary operation of the start switch 61a, the abovedescribed cycle of operation will be repeated. If, on the other hand, the first drying period has not been completed when the door switch 23 is opened, the relay cams 85438 are located at intermediate positions 180 from those shown in FIGURE 4. Upon reclosing of the door switch 23, the relay coil 83 is energized through the cam switch 90 to advance the cams 8588 another step. As the motor 11 cannot be energized through the open cam switch 91, the dryer will not operate. To resume operation of the dryer, it is necessary to reopen the door switch 23 to deenergize the relay coil 83. This causes the relay cams to step to their original positions shown in FIGURE 4. Upon reclosing of the door switch 23 and momentary operation of the start switch 61a, the dryer control system will repeat its entire operating cycle described above.

What is claimed is:

1. In a control system for a clothes drying machine having an electric motor for rotating a drum in order to tumble clothes contained therein to be dried, heater means including a heating unit for heating the interior of said drum in order to evaporate moisture from clothes therein, and spaced electrodes positioned within said drum and exposed to clothes therein in order to be electrically bridged by damp clothes tumbled in said drum; the combination therewith of;

an electric supply circuit including at least first and second supply lines;

a first relay having a first coil and first and second normally open switches closed upon energization of said first coil;

a heating unit energizing circuit including said first switch connecting said heating unit to said supply circuit;

a motor energizing circuit including said second switch connecting said motor to said supply circuit, said motor energizing circuit including means connecting said second switch to said first supply line;

a normally open momentary contact start switch connected to said first supply line;

means connecting said first coil between said start switch and said second supply line;

a second relay having a second coil, a third normally open switch closed upon energization of said second coil, and a fourth normally open sequence switch closed only upon alternate deenergization of said second coil;

a first shunt circuit connected in parallel with said start switch and including said second and third switches serially connected between said first supply line and the junction of said start switch and said first coil;

a second shunt circuit connected in parallel with said start switch and including said fourth switch connected between said first supply line and said junction;

means including a normally closed electrically controlled switching device connecting said second coil between said junction and said second supply line;

and a moisture-sensing circuit connected between said junction and said second supply line, said moisturesensing circuit including time delay means connected to said electrodes and controlling said switching device, said moisture-sensing circuit being responsive to the electrical resistance condition of the clothes engaging said electrodes to open said switching device only when the electrical resistance of the clothes is above a predetermined value for a predetermined period of time subsequent to each successive energization of said moisture-sensing circuit.

2. In a control system for a clothes drying machine having an electric motor for rotating a drum in order to tumble clothes contained therein to be dried, heater means including a heating unit for heating the interior of said drum in order to evaporate moisture from clothes therein, an interlock door switch operated by a door providing access to the interior of said drum and having contacts opened in response to the opening of said door, and spaced electrodes positioned within said drum and exposed to clothes therein in order to be electrically bridged by damp clothes tumbled in said drum; the combination therewith of:

an electric supply circuit including at least first and second supply lines;

a first relay having a first coil and first and second normally open switches closed upon energization of said first coil;

a heating unit energizing circuit including said first switch connecting said heating unit to said supply circuit;

a motor starting and running circuit connecting said second switch, said motor and said door switch in series across said first and second supply lines, said motor starting and running circuit including means connecting said second switch to said first supply line and means connecting said door switch to said second supply line;

a second motor running circuit connecting a thermostatic cooldown switch open at low temperatures, a speed-responsive switch closed at running speeds of said motor, said motor, and said door switch in series across said first and second supply lines;

a normally open momentary contact start switch connected to said first supply line;

an energizing circuit for said first coil connecting said start switch, said first coil and said door switch in series across said first and second supply lines;

a second relay having a second coil, a third normally open switch closed upon energization of said second coil, and a fourth normally open sequence switch closed only upon alternate deenergizations of said second coil;

a first shunt circuit connected in parallel with said start switch and including said second and third switches serially connected between said first supply line and the junction of said start switch and said first coil;

a second shunt circuit connected in parallel with said start switch and including said fourth switch connected between said first supply line and said junction;

means including a normally closed electrically controlled switching device connecting said second coil between said junction and said second supply line;

- and a moisture-sensing circuit connected between said junction and said second supply line, said moisture sensing circuit including time delay means connected to said electrodes and controlling said switching device, said moisture-sensing circuit being responsive to the electrical resistance condition of the clothes engaging said electrodes to open said switching device only when the electrical resistance of the clothes is above a predetermined value for a predetermined period of time subsequent to each successive energization of said moisture-sensing circuit.

3. The combination according to claim 2 in which said switching device comprises a fifth normally closed switch of a third delay having a third coil, said fifth switch being opened upon energization of said third coil, and said time delay means controlling the energization of said third coil.

4. The combination according to claim 3 in which said moisture-sensing circuit comprises:

a resistance-capacitance timing circuit including a rectifier, an adjustable resistor and a capacitor connected in series between said junction and said second supply line;

means connecting said electrodes in parallel with said capacitor whereby the capacitor is discharged by the engagement of damp clothes with said electrodes;

and a gaseous discharge device and said third coil in series and connected across said capacitor, said gaseous discharge device being normally non-conductive and becoming conductive when said capacitor has been charged to a predetermined potential for effecting current flow through said third coil.

5. The combination according to claim 4 in which:

said second relay includes a sixth normally closed switch opened upon energization of said second coil;

and a capacitor discharge circuit including said sixth switch connected in parallel with said capacitor.

6. The combination according to claim 2 in which:

said start switch comprises two sets of serially con nected normally open contacts; and

the junction of said sets of contacts is connected by a conductor to the junction of said second switch and said third switch.

7. In a control system for a clothes drying machine having an electric motor for rotating a drum in order to tumble clothes contained therein to be dried, heater means including a heating unit for heating the interior of said drum in order to evaporate moisture from clothes therein, and spaced electrodes positioned within said drum and exposed to clothes therein in order to the electrically bridged by damp clothes tumbled in said drum; the combination therewith of:

an electric supply circuit including at least first and second supply lines;

switching apparatus including first, second and third switch means and electric switch actuating means for selectively controlling the operation of said switch means; said first and second switch means each having an initially open condition prior to initial energization of said actuating means and having a closed condition during a subsequent energization, de-energization and re-energization of said actuating means; said third switch means having a closed condition when said actuating means is unenergized and an open condition when said actuating means is energized;

a heating unit energizing circuit including said first switch means connecting said heating unit to said supply circuit;

a time delay circuit including in series a resistor and a capacitor, said electrodes being connected across said capacitor to prevent substantial charging of said capacitor through said resistor when said electrodes are bridged by damp clothes, said capacitor charging to a predetermined voltage when the electrical resistance of the clothes bridging said electrodes is above a predetermined value for a predetermined period of time;

a normally open momentary start switch connecting said time delay circuit across said first and second supply lines and connecting said actuating means across said first and second supply lines;

means responsive to the voltage of said capacitor to de-energize said actuating means when said capacitor charges to said predetermined voltage;

conductor means connecting said second switch means in parallel with said start switch for connecting said time delay circuit and said actuating means to said supply circuit after initial energization of said actuating means by said start switch and during a subsequent de-energization and re-energization of said actuating means;

a capacitor discharge circuit including said third switch means connected in parallel with said capacitor to discharge said capacitor upon each de-energization of said actuating means.

8. In a control system for a clothes drying machine having an electric motor for rotating a drum in order to tumble clothes contained therein to be dried, heater means including a heating unit for heating the interior of said drum in order to evaporate moisture from clothes therein, and spaced electrodes positioned within said drum and exposed to clothes therein in order to be electrically bridged by damp clothes tumbled in said drum; the combination therewith of:

an electric supply circuit including at least first and second supply lines;

a stepping ratchet relay comprising a plurality of stepping switches including first and second stepping switches; ratchet means movable in a step-by-step manner from an initial position through at least three successive positions for selectively opening and closing said stepping switches; a magnet coil for actuation of said ratchet means to advance said ratchet means one step upon each energization of said magnet coil and one step upon each successive deenergization of said magnet coil; said first and second stepping switches being opened with said ratchet means at its initial position and being closed with said ratchet means at each of its three successive positions;

a heating unit energizing circuit including said first stepping switch connecting said heating unit to said supply circuit;

a time delay circuit including in series a resistor and a capacitor, said electrodes being connected across said capacitor to prevent substantial charging of said capacitor through said resistor when said electrodes are bridged by damp clothes, said capacitor charging to a predetermined voltage when the electrical resistance of the clothes bridging said electrodes is above a predetermined value for a predetermined period of time;

a normally open momentary start switch connecting said time delay circuit across said first and second supply lines and connecting said magnet coil across said first and second supply lines;

means responsive to the voltage of said capacitor to deenergize said magnet coil when said capacitor charges to said predetermined voltage; and

conductor means connecting said second stepping switch in parallel with said start switch for connecting said time delay circuit and said magnet coil to said sup- 1 1 '1 2 ply circuit after initial energization of said actuating ping switch being closed with said ratchet means at means by said start switch and during a subsequent its first successive position; deenergization and re-energization of said magnet a motor starting and running circuit including said coil. fourth stepping switch connecting said electric motor 9. The combination according to claim 8 including: across said first and second supply lines; and a third stepping switch controlled by said ratchet means; a second motor running circuit including a thermosaid third stepping switch being closed with said static cool down switch open at low temperatures ratchet means at its initial position and at its second and aspeed-responsive switch closed at running speeds successive position; said third stepping switch being of said electric motor connecting said electric motor opened with said ratchet means in its first and third 10 across said first and second supply lines.

successive positions; and

a capacitor discharge circuit including said third switch References Cted by the Examiner means connected in parallel with said capacitor to UNITED STATES PATENTS discharge said capacitor upon each de-energization 2,796,679 6/1957 Dunnelman 34, 45

of 531d f f 3,180,038 4/1965 Chafee 34 10. The com b1nat1on according to claim 8 mcludmg: 3,197834 8/1965 Smith 34 45 a fourth stepping switch operated by said ratchet means; 3 17 1 5 Mallinger 5 said fourth stepping switching being opened with said ratchet means at its initial position and at its sec FREDERICK MATTEsONJR" PHmm'Y Exammfl- 0nd and third successive positions; said fourth step- 20 D. A. TAMBURRO, Assistant Examiner. 

1. IN A CONTROL SYSTEM FOR A CLOTHES DRYING MACHINE HAVING AN ELECTRIC MOTOR FOR ROTATING A DRUM IN ORDER TO TUMBLE CLOTHES CONTAINED THEREIN TO BE DRIED, HEATER MEANS INCLUDING A HEATING UNIT FOR HEATING THE INTERIOR OF SAID DRUM IN ORDER TO EVAPORATE MOISTURE FROM CLOTHES THEREIN, AND SPACED ELECTRODES POSITIONED WITHIN SAID DRUM AND EXPOSED TO CLOTHES THEREIN IN ORDER TO BE ELECTRICALLY BRIDGED BY DAMP CLOTHES TUMBLED IN SAID DRUM; THE COMBINATION THEREWITH OF; AN ELECTRIC SUPPLY CIRCUIT INCLUDING AT LEAST FIRST AND SECOND SUPPLY LINES; A FIRST RELAY HAVING A FIRST COIL AND FIRST AND SECOND NORMALLY OPEN SWITCHES CLOSED UPON ENERGIZATION OF SAID FIRST COIL; A HEATING UNIT ENERGIZING CIRCUIT INCLUDING SAID FIRST SWITCH CONNECTING SAID HEATING UNIT TO SAID SUPPLY CIRCUIT; A MOTOR ENERGIZING CIRCUIT INCLUDING SAID SECOND SWITCH CONNECTING SAID MOTOR TO SAID SUPPLY CIRCUIT, SAID MOTOR ENERGIZING CIRCUIT INCLUDING MEANS CONNECTING SAID SECOND SWITCH TO SAID FIRST SUPPLY LINE; A NORMALLY OPEN MOMENTARY CONTACT START SWITCH CONNECTED TO SAID FIRST SUPPLY LINE; MEANS CONNECTING SAID FIRST COIL BETWEEN SAID START SWITCH AND SAID SECOND SUPPLY LINE; A SECOND RELAY HAVING A SECOND COIL, A THIRD NORMALLY OPEN SWITCH CLOSED UPON ENERGIZATION OF SAID SECOND COIL, AND A FOURTH NORMALLY OPEN SEQUENCE SWITCH CLOSED ONLY UPON ALTERNATE DEENERGIZATION OF SAID SECOND COIL; A FIRST SHUNT CIRCUIT CONNECTED IN PARALLEL WITH SAID START SWITCH AND INCLUDING SAID SECOND AND THIRD SWITCHES SERIALLY CONNECTED BETWEEN SAID FIRST SUPPLY LINE AND THE JUNCTION OF SAID START SWITCH AND SAID FIRST COIL; A SECOND SHUNT CIRCUIT CONNECTED IN PARALLEL WITH SAID START SWITCH AND INCLUDING SAID FOURTH SWITCH CONNECTED BETWEEN SAID FIRST SUPPLY LINE AND SAID JUNCTION; MEANS INCLUDING A NORMALLY CLOSED ELECTRICALLY CONTROLLED SWITCHING DEVICE CONNECTING SAID SECOND COIL BETWEEN SAID JUNCTION AND SAID SECOND SUPPLY LINE; AND A MOISTURE-SENSING CIRCUIT CONNECTED BETWEEN SAID JUNCTION AND SAID SECOND SUPPLY LINE, SAID MOISTURESENSING CIRCUIT INCLUDING TIME DELAY MEANS CONNECTED TO SAID ELECTRODES AND CONTROLLING SAID SWITCHING DEVICE, SAID MOISTURE-SENSING CIRCUIT BEING RESPONSIVE TO THE ELECTRICAL RESISTANCE CONDITION OF THE CLOTHES ENGAGING SAID ELECTRODES TO OPEN SAID SWITCHING DEVICE ONLY WHEN THE ELECTRICAL RESISTANCE OF THE CLOTHES IS ABOVE A PREDETERMINED VALUE FOR A PREDETERMINED PERIOD OF TIME SUBSEQUENT TO EACH SUCCESSIVE ENERGIZATION OF SAID MOISTURE-SENSING CIRCUIT. 